A filter plate composed of a thermoplastic material is known for a filter press in which a plurality of these filter plates are clamped together edgewise forming a plurality of filter chambers between them.
Each of the filter plates has a press wall on one or both sides of it. This press wall is flexible and is movable by action of a pressurizing medium into one of the filter chambers. Each of the filter plates includes a supporting wall and a compression chamber for the pressurizing medium acting on the press wall, the supporting wall being located between adjacent compression chambers.
A filter plate assembled from five plate parts, comprising two plate frames, two press walls or membranes and a supporting wall, is described in German Pat. No. 34 14 550. A locking or catch device is provided for attaching the plate frame with the supporting wall on the surfaces of both parts facing each other.
The press wall formed separately from the plate frames is inserted edgewise in a clamping gap running in the circumferential direction between the supporting wall and one of the plate frames. A sealing gap directed exteriorly widened transverse to the plane of the filter plate is connected to this clamping gap at a shoulder surface opposing the clamping gap. The press wall engages with a shaped or special cross sectioned edge in this sealing gap which prevents the press wall from sliding out of the clamping gap.
This known filter plate of course allows the plate frame and the press wall to be designed in regard to their material properties according to the requirements of the filter press. Thus a very reliable operation and besides a wider range of application in regard to filtrate properties results.
However this known filter plate is very costly to manufacture and is time consuming to assemble. Furthermore, there is danger that filtration products will deposit between the elastic press wall and the plate frame in the vicinity of the clamping gap. This is particularly disturbing when filtrates of different composition are introduced in succession into the filter press. Filtration residues of a first filtration can then be carried off in a subsequent filtration.